mirror: Fix performance problem by using bufferred channels.

The problem was that statusCh, queues were all waiting on the
select for too long. This is the nature of things in Go.

Using bufferred channel increases the performance as expected.

Fixes #1908

cmd/cp-main.go

@@ -315,7 +315,7 @@ func doCopySession(session *sessionV8) {
 	}
 
 	// Wait on status of doCopy() operation.
-	var statusCh = make(chan URLs)
+	var statusCh = make(chan URLs, 10000)
 
 	// Add a wait group.
 	var wg = new(sync.WaitGroup)

cmd/mirror-main.go

@@ -712,8 +712,8 @@ func newMirrorSession(session *sessionV8) *mirrorSession {
 		trapCh:    signalTrap(os.Interrupt, syscall.SIGTERM),
 		sessionV8: session,
 
-		statusCh:  make(chan URLs),
-		harvestCh: make(chan URLs),
+		statusCh:  make(chan URLs, 10000),
+		harvestCh: make(chan URLs, 10000),
 		errorCh:   make(chan *probe.Error),
 
 		watcher: NewWatcher(session.Header.When),

cmd/queue.go

@@ -45,7 +45,7 @@ type Queue struct {
 // NewQueue creates a new queue
 func NewQueue() *Queue {
 	return &Queue{
-		idleCh: make(chan interface{}),
+		idleCh: make(chan interface{}, 10000),
 		closed: false,
 	}
 }